Boiling and Pressure

Mountain top boiling

If you were on a mountain top you would find the water in a kettle would start boiling at less than 100 °C.

Why? Because the air pressure is much lower the higher up you are – and the lower the pressure the lower the temperature at which liquids boil.

You can change the temperature at which any liquid boils by changing the pressure. Boiling at a particular pressure is known as Vaporization or Evaporation.

For example, in your fridge at home a liquid (known as a refrigerant) is circulated through pipework at the back. The space inside the fridge is cooled when this liquid refrigerant evaporates at low pressure drawing heat from the space inside.

The evaporated gas is re-pressurised by a motor and turns back to a liquid in a continuous circuit.